The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed inventions, or that any publication specifically or implicitly referenced is prior art.
HSP90s are ubiquitous chaperone proteins that are involved in folding, activation and assembly of a wide range of proteins, including key proteins involved in signal transduction, cell cycle control and transcriptional regulation. Researchers have reported that HSP90 chaperone proteins are associated with important signaling proteins, such as steroid hormone receptors and protein kinases, including, e.g., Raf-1, EGFR, v-Src family kinases, Cdk4, and ErbB-2 (Buchner J., 1999, TIBS, 24:136-141; Stepanova, L. et al., 1996, Genes Dev. 10:1491-502; Dai, K. et al., 1996, J. Biol. Chem. 271:22030-4). Studies further indicate that certain co-chaperones, e.g., Hsp70, p60/Hop/Sti1, Hip, Bag1, HSP40/Hdj2/Hsj1, immunophilins, p23, and p50, may assist HSP90 in its function (see, e.g., Caplan, A., Trends in Cell Biol., 9: 262-68 (1999).
Ansamycin antibiotics, e.g., herbimycin A (HA), geldanamycin (GM), and 17-AAG are thought to exert their anticancerous effects by tight binding of the N-terminus pocket of HSP90, thereby destabilizing substrates that normally interact with HSP90 (Stebbins, C. et al., 1997, Cell, 89:239-250). This pocket is highly conserved and has weak homology to the ATP-binding site of DNA gyrase (Stebbins, C. et al., supra; Grenert, J. P. et al., 1997, J. Biol. Chem., 272:23843-50). Further, ATP and ADP have both been shown to bind this pocket with low affinity and to have weak ATPase activity (Proromou, C. et al., 1997, Cell, 90: 65-75; Panaretou, B. et al., 1998, EMBO J., 17: 4829-36). In vitro and in vivo studies have demonstrated that occupancy of this N-terminal pocket by ansamycins and other HSP90 inhibitors alters HSP90 function and inhibits protein folding. At high concentrations, ansamycins and other HSP90 inhibitors have been shown to prevent binding of protein substrates to HSP90 (Scheibel, T., H. et al., 1999, Proc. Natl. Acad. Sci. USA 96:1297-302; Schulte, T. W. et al., 1995, J. Biol. Chem. 270:24585-8; Whitesell, L., et al., 1994, Proc. Natl. Acad. Sci. USA 91:8324-8328). Ansamycins have also been demonstrated to inhibit the ATP-dependent release of chaperone-associated protein substrates (Schneider, C., L. et al., 1996, Proc. Natl. Acad. Sci. USA, 93:14536-41; Sepp-Lorenzino et al., 1995, J. Biol. Chem. 270:16580-16587). In either event, the substrates are degraded by a ubiquitin-dependent process in the proteasome (Schneider, C., L., supra; Sepp-Lorenzino, L., et al., 1995, J. Biol. Chem., 270:16580-16587; Whitesell, L. et al., 1994, Proc. Natl. Acad. Sci. USA, 91: 8324-8328).
HSP90 substrate destabilization occurs in tumor and non-transformed cells alike and has been shown to be especially effective on a subset of signaling regulators, e.g., Raf (Schulte, T. W. et al., 1997, Biochem. Biophys. Res. Commun. 239:655-9; Schulte, T. W., et al., 1995, J. Biol. Chem. 270:24585-8), nuclear steroid receptors (Segnitz, B., and U. Gehring. 1997, J. Biol. Chem. 272:18694-18701; Smith, D. F. et al., 1995, Mol. Cell. Biol. 15:6804-12), v-src (Whitesell, L., et al., 1994, Proc. Natl. Acad. Sci. USA 91:8324-8328) and certain transmembrane tyrosine kinases (Sepp-Lorenzino, L. et al., 1995, J. Biol. Chem. 270:16580-16587) such as EGF receptor (EGFR) and Her2/Neu (Hartmann, F., et al., 1997, Int. J. Cancer 70:221-9; Miller, P. et al., 1994, Cancer Res. 54:2724-2730; Mimnaugh, E. G., et al., 1996, J. Biol. Chem. 271:22796-801; Schnur, R. et al., 1995, J. Med. Chem. 38:3806-3812), CDK4, and mutant p53. Erlichman et al., Proc. AACR (2001), 42, abstract 4474. The ansamycin-induced loss of these proteins leads to the selective disruption of certain regulatory pathways and results in growth arrest at specific phases of the cell cycle (Muise-Heimericks, R. C. et al., 1998, J. Biol. Chem. 273:29864-72), and apoptosis, and/or differentiation of cells so treated (Vasilevskaya, A. et al., 1999, Cancer Res., 59:3935-40).
In addition to anti-cancer and antitumorgenic activity, HSP90 inhibitors have also been implicated in a wide variety of other utilities, including use as anti-inflammation agents, anti-infectious disease agents, agents for treating autoimmunity, agents for treating ischemia, and agents useful in promoting nerve regeneration (See, e.g., Rosen et al., WO 02/09696; PCT/US01/23640; Degranco et al., WO 99/51223; PCT/US99/07242; Gold, U.S. Pat. No. 6,210,974 B1). There are reports in the literature that fibrogenic disorders including but not limited to scleroderma, polymyositis, systemic lupus, rheumatoid arthritis, liver cirrhosis, keloid formation, interstitial nephritis, and pulmonary fibrosis may be treatable. (Strehlow, WO 02/02123; PCT/US01/20578).
Ansamycins and other HSP90 inhibitors thus hold great promise for the treatment and/or prevention of many types of disorders. However, their relative insolubility makes them difficult to formulate and administer, and they are not easily synthesized and currently must, at least in part, be generated through fermentation. Further, the dose limiting toxicity of ansamycins is hepatic. Despite the potential of ansamycins, alternative HSP90 inhibitors are therefore needed.
Recently, Chiosis et al. described the design and synthesis of purine analogs that mimic geldanamycin and other ansamycins in their ability to bind the ATP binding pocket of, and thus inhibit, HSP90. See International Patent Application PCT/US01/46303 (WO 02/36075; Chemistry & Biology 8:289-299 (2001). The specific compounds that Chiosis et al. described included a trimethoxybenzyl entity substituted at positions 3,4, and 5. Using gel-binding assays, these were shown to bind HSP90 approximately 20-fold less avidly than the benzoquinone ansamycin, 17-AAG. Chiosis et al. did not attempt a quinone mimic for the methoxybenzyl entity, speculating that to do so would lead to hepatoxicity. Id., pg. 290, col. 1, ¶ 4. Nor did Chiosis et al. teach, suggest, or otherwise report the use of sulfides, sulfoxides, and sulfones as described herein.